4b: Crude oil

what is crude oil

a mixture of different hydrocarbons of similar chain length called fractions

how do the physical properties of hydrocarbons change as the molecule size increases

* boiling point increases
* liquid becomes less volatile, more viscous and darker
* don’t burn as easily

why do the physical properties of hydrocarbons change as the molecule size increases

* increasing attraction between molecules
* more energy needed to break intermolecular forces

how are the fractions in crude oil separated

by fractional distillation

does the number of carbon atoms in a chain affect properties and boiling points

yes

what is the determining factor for fractional distillation

size and length of each hydrocarbon molecule

what does the size of each hydrocarbon molecule depend on

number of carbon and hydrogen atoms the molecule contains

fractional distillation

* crude oil is heated and vapour is passed into a fractionating column
* the vapour rises up depending on its boiling point

positioning of crude oil in a fractionating column

cool at the top and hot at the bottom

do smaller molecules have lower boiling points or higher

lower

do larger molecules have lower boiling points or higher

higher

what are the different heights that the different fractions condense at dependent on

their boiling points

order of main fractions from coolest to hottest

* refinery gas
* gasoline
* kerosene
* diesel oil
* fuel oil
* bitumen

what is refinery gas

a mixture of methane, ethane, propane, butane

uses of refinery gas

used for LPG for domestic heating and cooking

uses of gasoline

fuel in cars

uses of kerosene

fuel for jet aircrafts, domestic heating oil and paraffin

uses of diesel

fuel for buses, lorries, cars, railway engines and conversion into petrol for cracking

uses of fuel oil

fuel for ships and industrial heating

uses of bitumen

melted and mixed with small pieces of rock to make the top surface of roads

what is a fuel

a substance which when burnt releases heat energy

fossil fuels

* coal
* oil
* natural gas
* oil shales
* tar sands

how are non-renewable fossil fuels obtained

from fractional distillation in crude oil

combustion - products

* carbon dioxide
* carbon monoxide
* oxides of nitrogen
* oxides of sulfur
* unburned hydrocarbons
* carbon particulates

complete combustion in hydrocarbon compounds

* occurs in the presence of excess oxygen
* a hydrocarbon burns in air to form carbon dioxide and water
* it also releases heat

incomplete combustion in hydrocarbon compounds

* occurs in presence of insufficient oxygen
* it releases soot, carbon monoxide and water

carbon monoxide

toxic and odourless gas causing death

what are the dangers of carbon monoxide

it reduces the ability of the blood to carry oxygen around the body by binding to haemoglobin

how is carbon dioxide harmful for the environment

it’s a greenhouse gas which traps heat radiated from the earth’s surface

what is formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces

NO and NO2

acid rain

formed when water and oxygen in the atmosphere react with sulfur dioxide to product sulfuric acid, or various nitrogen oxides to give nitric acid

how do fossil fuels contribute to acid rain

* they contain a small amount of sulfur which is burned with the fuel and forms sulfur dioxide
* this reacts in the atmosphere with oxygen and water and becomes sulfuric acid
* nitrogen dioxide from car engine reacts with rain water to form nitrous and nitric acids